Elektrik ark kaynağı ve toz püskürtme yöntemleri ile zırhlanan parçaların, abrezif aşınma davranışlarının incelenmesi

Abstract

Bu çalışmada ; sanayinin en büyük problemi olan aşınmaya karşı dayanıklı yüzey sağlanması amacıyla kullanılan yüzey kaplama alaşımlarının aşınma davranışları, herhangi bir işlem yapılmamış St 37 malzeme baz alınarak incelenmiştir. Yüzey malzemesi olarak ; Nikel ve Demir esaslı alaşımlar seçilmiş ve bu alaşımlar, St 37 malzeme üzerine, elektrik ark kaynak ve yanıcı gaz toz püskürtme yöntemleriyle uygulanmıştır. Seçilen yüzey kaplama malzemeleri aşağıda belirtildiği gibidir. 1) Ni - Cr, B, Si tek kademeli sıcak toz püskürtme alaşımı, 2) Ni - Cr, B, Si + W2C tek kademeli sıcak püskürtme alaşımı, 3) Ni - Cr, B, Si çift kademeli sıcak püskürtme alaşımı, 4) Ni - Cr, B, Si + WC / Co çift kademeli sıcak püskürtme alaşımı, 5 ) St 37 malzeme (Fe-0,2 C: 0,12 P + S) 6) Yüksek kromlu martenzitik çelik ( Fe - 1 0 Cr : 1 Mn : 0,4 C), 7) Yüksek kromlu kompleks demir ( Fe - 33 Cr : 3 C ), 8) Yüksek kromlu ostenitik demir ( Fe - 40 Cr : 6 C ). St 37 malzeme dahil olmak üzere sekiz adet numunenin abrezif aşınma davranışları ; SiC ( P 80 ) esaslı zımpara ile pim - disk aşınma düzeneğinde numunelerin ağırlık kayıpları, değişen kayma ( temas ) hızlarına göre incelenmiştir. Yapılan deneyler sonucunda, uygulanan yüzey kaplama işlemlerinin St 37 malzemenin aşınma direncini arttırdığı saptanmıştır. En iyi sonuçları, Tungsten karbür içeren Nikel esaslı sıcak püskürtme alaşımları olan 2. ve 4. nolu malzemeler sağlamıştır. Abrezif aşınma dayınımı için ; aşınmaya maruz kalan yüzeyin iç yapısının oldukça önemli olduğu ve karbür, nitrür gibi sert fazlar içeren malzemelerin kullanılmasının gerektiği ortaya çıkmış ve yapıdaki, sert partiküllerin sertlik, boyut ve miktarlarının artışının, aşınma direnciyle direk orantılı olduğu saptanmıştır. Abrezif aşınma dayanımı için kullanılacak Tungsten karbürlü, Nikel matriksli sert kaplama alaşımları üreticiler tarafından, tel, tüp, elektrod ve toz püskürtme tozlan şeklinde sunmaktadırlar. Bu alaşımlann uygulanmasında ise oksi - asetilen ve / veya toz püskürtme v jya elektrik ark kaynağı yöntemleri kullanılabilir, incelenen numunelerin hazırlanmasında püskürtme yönteminin avantajı daha hassas ve ince kaplamanın yapılabilmesidir. Elektrik ark kaynak yönteminin kullanılmasının en büyük dezavantaj ise, mevcut karbürlerin ergime riskidir. Deneyler sonucunda elde edilen diğer bir husus ise ; aşınma mekanizmasını etkileyen faktörlerden, kayma ( temas ) hızının artışı aşınma miktarı ile doğru orantılı olduğu gözlenmiştir. Fakat, literatürde bu orantının belirli bir değere kadar olduğu ve bu değerin üstündeki hızlar için aşınma miktarının sabit kaldığı belirtilmektedir. Deneylerin gerçekleştirildiği düzeneğin maksimum hızı bu değerin altıda kaldığı için bu sonuç gözlenememiştir.

True cost to the world's economy of Industrial wear's virtually inestimable. The direct cost of replacing component base metal ( % 2 in weight of produced annually), together with the labour cost of producing the parts and labour cost of refitting, amount to thousands of billions of Dollars to which must be added such indirect cost as production losses due to down time cost due to inefficiency of worn machinery to rate of factory rejects, energy wastage, etc. The total must come to billions of Dollars. It is the aim of every company to improve productivity and efficiency and indeed both men and machines can be made to perform better and make better use their environmental and working conditions. Protective maintenance is one of the important ways to make the best use of machine parts and to prevent serious damage to expensive equipment. In machine industry, wear phenomena are taken into consideration at design stage, the cost - effectiveness of any solution being a major criterion. Welding and metal coating occupy a leading position among modern techniques for prolonging the service life of key machine parts, due to the case and flexibility with which they can be applied. Wear, generally defined as a progressive looser displacement of materials from surface a result of relative motion between that surface and another, serious defects are created in the surface. Wear, is destruction of surface materials in machines, tools and other instruments General definition, embracing a range of phenomena which can either be found separately or in combinations. wear causes shut - down of machinery, requires stocking of spare parts, occupies operative's time ( dismantling, re assembly ) Production cost which it is clearly in every one ' s interest to reduce, with anti wear coating which offer the longest possible service life. In each case, it will be necessary to determine the principal causes of wear, to guide our choice to an appropriate solution with maximum benefit. Those cause as follows ; - Wear due to predominantly mechanical factors 1 ) Abrasion 2) Cavitation 3) Adhesion 4) Plastic deformation ( contact fatigue) - Wear due to chemical factors : 1 ) Corrosion - Wear due to granular solids : 1 ) Abrasion 2) Erosion Abrasion causes the most severe damage than others. Abrasive wear arise from the penetration of one surface by harder body or surface ; damage involves a cutting or ploughing action. It may involve particle moving over a surface ( two body abrasion ), hard particle moving over two moving surface ( three body abrasion ) or a roughened surface moving over and penetrating an opposing surface. In practise, abrasion is often considered under separate headings, such as, gouging, scoring, low stress, high stress, etc.,but these identify the, severity, rather than the type of wear ; in all the basic abrasive action is similar. wS In relation to type of particle and the carrying fluid ; a) Granular solids : gravel - sand - ash, e.g. shovel. b) Granular solids in plastic mass : clay, loam or similar e.g. ploughshare. c) Particle suspended in liquid : e.g. hydraulic pump. d) Particle suspended in gas : e.g. fan. The term " abrasion " then, is reserved for different types of damages to surfaces, metal or plastic, caused by hand and granular foreign bodies. The degree of abrasive resistance of any materials is measured in relative, not absolute, values by composition either with given reference materials or with the same materials in a standardised structural state. In seeking, abrasion resistant materials, it is necessary to ensure there is sufficient strength to resist imposed stresses from the wear mechanism and sufficient toughness to withstand impact For in pure abrasion, the ideal structrure tent to be hard matrix ( e.g. martensite 9 with evenly distrubuted hard particles ( e.g. carbides ). If there is a large amount of impact loading, tahn it may be necessary to revert to a tougher matrix ( e.g. bainite ) at expense of some wear resistance, or possibly use an initially relatively soft matrix that transform during service / e.g. unstable austenite ) This dual requirement for strength and toughness demands a compromise. There is any doubt, the balance should be titled in favour of extra toughness ; a higher than optimum wear rate reduces component life but less disastrously than component fracture. In this study, abrasion wear resistance of Ni base alloys, which are applied by fusion and hot powder spraying system and Fe base alloys, which are applied electrical arc welding, on St 37 standard steel pirn, are tested wear phenomena. Tested materials are followed ; 1 ) Ni :; Cr, B, Si,Fe Fusion powder spraying alloys. ( Spraying and fusion simultaneously ), 2) Ni ; Cr, B, Si, Fe + W2C Fusion spraying alloys. 3) Ni ; Cr, B, Si, Fe Hot powder spraying alloys. ( Firtsly spraying, after than fusioning ) 4) Ni ; Cr, B, Si, Fe + WC / Co Hot powder spraying alloys. 5) St 37 Steel (Fe; 0,02 C %,12 P + S %) 6) High chromium martensitic steel ( Fe ; 1 0 Cr%, 1 Mn %, 0,4 C 7) High chromium complex iron ( Fe ; 33 Cr %, 3 C % ) 8) High chromium austenitic iron ( Fe ; 40 Cr %, 6 C % ) Specimens are prepared by coated above alloys on St 37 pirn, which is 1 0 mm diameter and 20mm long as a cylindrical shape, using by powder spraying and electrical arc welding processes. Prepared specimens are tested on two body abrasion tester, called pirn on disk apparatus, with SiC based abrasive paper, which is P 80 D type. Experiments are carried out in 3 group with below parameters. Each experiment takes 45 minutes and every quarter minutes changed the abrasive paper and measured weight of specimen, during experiment. After experiment found total weight losses of each materials for each group. viil finally, relative abrasion rate and abrasion resistance of materials are calculated from using by bellows equations. Wa : Wear Rate (mm3/Nm) AG G : Total weight loss (mg) Wa = d : Density of material ( g/cm3) d * L * D L : Load (N) D : Sliding distance (m) 1 Wr= Wr: Wear resistance (Nm/m m 3) Wa After experimental studies, these result is observed that, Ni based surface coating alloys, which were applied powder spraying system, have been increased abrasion wear resistance. The best result was given by Ni based, Cr, B, Si, Fe with consisting Tungsten carbide alloys. During experiments, two types Ni based alloys with tungsten carbide surface coatings, which contain % 60 W2C ( specimen number : 2) and % 48 WC/Co (4) have tested. Although both coatings had same matrix composition, powder sizes were different. Wear resistance of Ni based Cr, B, Si, Fe with %48 WC/Co alloys is better then other. The other tested both coatings had same composition and different particle size together and same other specimen' matrix. The smaller powder size coating, which was applied by hot spraying system, has given better result then the greater powder size coating, which was applied fusion spraying system. Briefly, abrasion wear experiments have been shown that, wear resistance of consisting greater Tungsten carbide particles with smaller particle matrix Ni based surface coating powder was better then other surface coating Ni based powder. So, carbide particle size into coating is important and should be greater. In addition, Ni based alloys with Tungsten carbide coatings had better wear resistance then High chromium complex and austenitic iron and high Chromium martensitic steel coating. That result indicates that, carbide type into coating is also important in order to resistance to abrasion. In other result that, when sliding velocity has been increased, wear rate would have been raised, too. In literature, wear losses are increased up to a sliding velocity value, but if sliding velocity is greater than that value, wear losses will be fixed. Since, experiment had been carried out on the smaller sliding velocity abrasion test apparatus, that result had been not observed, completely.